Gauzes, powders, sprays, ointments, creams, sponges and the like have so far been used as therapeutic dressings for a wound surface. Most of them serve to absorb exudates from a wound surface to thereby dry the wound area and promote the healing thereof. In recent years, however, it has been revealed that a wound healing promoting effect can be produced by allowing the exudate to remain on the wound surface to thereby maintain the wound area in an appropriately moist environment rather than by drying the wound area; the necessity of maintaining the wound area in an appropriately moist environment has thus been recognized, and certain wound-covering materials suited therefor have been developed.
The conditions required of a wound-covering material include, among others, absorbency, moisture-maintaining ability, bacterial invasion preventing ability, bacterial growth inhibiting ability, mechanical strength, adhesiveness, and transparency. The term “mechanical strength” means that the wound-covering material will not be disintegrated even after absorption of exudate and will not leave fragments thereof on the wound area on the occasion of replacement. Transparency is required so that the affected site may be observed by the eye.
The known wound-covering materials include polyurethane films, hydrocolloids, PVA hydrogels, and alginate gels, among others.
Among the wound-covering materials mentioned above, wound-covering materials prepared by spreading an acrylic adhesive on a polyurethane film are excellent in stretchability, but have no absorbency of exudate at all; therefore, when applied to the exuding wound surface, they allow fluid accumulation to occur, whereupon drainage becomes necessary. Furthermore, they have strong tackiness, so that they may cause pain and/or damage the regenerated skin on the occasion of replacement (cf. Patent Documents 1, 2 and 3).
Hydrocolloids absorb exudates as a result of swelling of hydrophilic colloid particles contained in a hydrophobic base and, therefore, they are excellent in absorbency; however, they tend to leave gel-like substance residues on the wound surface on the occasion of replacement. Further, many of them are semi-transparent or nontransparent, making them difficult to observe the wound surface. Furthermore, they are strong in tackiness, so that they may cause pain and/or damage the regenerated skin on the occasion of replacement.
PVA hydrogels contain about 80% of purified water in each preparation and, therefore, they are really excellent in maintaining moist environments, in alleviation of pain due to cooling effect and in transparency; however, they have little tackiness, so that fixation members such as bandages or surgical tapes are required. A proposal has been made to subject PVA hydrogels to such a treatment as exposure to radiation so that they may acquire tackiness (cf. Patent Document 4); however, the tackiness is still unsatisfactory.
Alginate gels are excellent in hemostatic effect and absorbency of exudate; since, however, the gelation is caused by exudates, a gel-like substance tends to remain on the wound surface on the occasion of replacement; moreover, since they build up open systems, it becomes necessary to cover them with a film material for the purpose of moisture maintenance, bacterial invasion prevention and bacterial growth inhibition (cf. Patent Document 5).
Therefore, a wound covering hydrogel material has been desired for which is excellent in stretchability and absorbs exudate, can maintain a moist environment suited for promoting the healing of the wound surface for a prolonged period of time and hardly causes pain or give a damage to the regenerated skin on the occasion of replacement of the wound-covering material with a new one.    Patent Document 1: Japanese Patent Publication A 58-87153    Patent Document 2: Japanese Patent Publication A 4-272765    Patent Document 3: Japanese Patent Publication A 2006-61263    Patent Document 4: Japanese Patent No. 3773983    Patent Document 5: Japanese Patent Publication A 8-187280